An exemplary information recording medium having a sector structure is an optical disc. As the recording density and the capacity of optical discs have improved recently, real time data including audio data and/or video data is recorded and edited for an increasing range of uses.
Conventional simultaneous reproduction of audio data and video data which is performed using cut-editing will be described.
First, with reference to FIG. 16, a reproduction apparatus 660 for simultaneously reproducing two pieces of real time data will be described. The reproduction apparatus 660 shown in FIG. 16 includes a pickup 654 for recording data to or reproducing real time data from an information recording medium (optical disc) 655, a reproduction buffer A 650 for accumulating real time data 656 which is read from the information recording medium 655, a decoder A 651 for decoding the real time data 656 accumulated in the reproduction buffer A 650, a reproduction buffer B 652 for accumulating real time data 657 which his read from the information recording medium 655, and a decoder B 653 for decoding the real time data 657 accumulated in the reproduction buffer B 652.
In simultaneous reproduction, when data from an information recording medium is read, the data is accumulated in the reproduction buffer. Unless the reproduction buffer becomes empty while the seek operation of the pickup, reproduction of the real time data is not interrupted. In the reproduction apparatus 660 shown in FIG. 16, “Vt” represents the data transfer rate between the pickup 654 and the reproduction buffer A 650 and between the pickup 654 and the reproduction buffer B 652. “Vd” represents the data transfer rate between the reproduction buffer A 650 and the decoder A 651 and between the reproduction buffer B 652 and the decoder B 653. (The data transfer rate between the reproduction buffer A 650 and the decoder A 651 may be represented by “Vd1”, and the data transfer rate between the reproduction buffer B 652 and the decoder B 653 may be represented by “Vd2”).
FIG. 17 shows an exemplary method of cut-editing which is performed on a continuous recorded area by a unit including a plurality of pieces of audio data and a plurality of pieces of video data. According to cut-editing, read start points (referred to as “in” point) and read finish points (“out” points) are sequentially set in real time data which has been recorded on an information recording medium such that a plurality of recorded areas of the data can be sequentially reproduced. In this example, recorded areas of audio data and video data are not determined based on full-seek time but based on short-distance access conditions such as, for example, fine-seek time. In the case where an access operation from the innermost portion to the outermost portion is necessary in the cut-editing, a full-seek operation is made possible after the plurality of recorded areas of the data are reproduced.
In FIG. 17, recorded areas G10, G12 and G14 in which video data is recorded, and recorded areas G11, G13 and G15 in which audio data is recorded, are located alternately from an inner portion to an outer portion of the information recording medium. Although not shown, a plurality of recorded areas may be present between recorded area G13 and recorded area G14. As shown in FIG. 17, “in” points IG10 and IG11 are set for the data recorded in the recorded areas G10 and G11, respectively. Also shown in FIG. 17, “out” points OG14 and OG15 are set for the data recorded in the recorded areas G14 and G15, respectively. The recorded area G16 is a part of the recorded area G10, and the recorded area G17 is a part of the recorded area G11. The recorded area G18 is a part of the recorded area G14, and the recorded area G19 is a part of the recorded area G15. The recorded area G16 is an area in the recorded area G10 from the position at which the “in” point IG10 is set to the end of the recorded area G10. The recorded area G17 is an area in the recorded area G11 from the position at which the “in” point IG11 is set to the end of the recorded area G11. The recorded area G18 is an area in the recorded area G14 from the beginning of the recorded area G14 to the position at which the “out” point OG14 is set. The recorded area G19 is an area in the recorded area G15 from the beginning of the recorded area G15 to the position at which the “out” point OG15 is set.
With reference to part (a) of FIG. 17, the conditions, for allowing the audio data and the video data to be simultaneously reproduced even when seek operations (part (b) of FIG. 17) are performed after the data recorded from recorded areas G16, G17, G12, G13 to the recorded areas G18 and G19 is reproduced, will be described.
Part (b) of FIG. 17 schematically shows the seek operations of the pickup. An access time includes a read time R31 of the recorded area G16, a seek time Tf1, a read time R32 of the recorded area G17, a seek time Tfi, a read time RV of the recorded area G12, a seek time Tfj, a read time RA of the recorded area G13, a seek time Tf2, a read time R33 of the recorded area G18, a seek time Tf3, a read time R34 of the recorded area G19, and a seek time Ta. It is assumed that a plurality of recorded areas are present between the recorded area G13 and the recorded area G18. Thus, it is assumed that total read time of the recorded areas G12 and G13 and the plurality of recorded areas is equal to the time required for reading the recorded areas G12 and G13 P times. A seek time from the recorded area of the video data to the recorded area of the audio data is represented by Tfj, and a seek time from the recorded area of the audio data to the recorded area of the video data is represented by Tfi. The seek time Tf; and the seek time Tfi, which correspond to the positions of the recorded areas which are present between the recorded area G13 and the recorded area G18, are represented by letters i and J.
Net read times from the information recording medium corresponding to the read times R31, R32, RV, RA, R33, and R34 are TinV, TinAa, TcV, AcAa, ToutV, and ToutAa, respectively.
The conditions regarding the video data are represented by the following expressions.YV÷VdV≧(TinV+Tf1+TinAa+P×(TcV+Tfj+Tfi+TcAa)+Tf2+ToutV+Tf3+ToutAa)+Ta+(P+2)×(a+b)×Ts)YV=(TinV+P×TcV+ToutV)×Vt 
The conditions regarding the audio data are represented by the following expressions.YA÷VdA≧(TinV+Tf1+TinAa+P×(TcV+Tfj+Tfi+TcAa)+Tf2+ToutV+Tf3+ToutAa)+Ta+(P+2)×(a+b)×Ts)YA=(TinAa+P×TcAa+ToutAa)×Vt 
The conditions for the simultaneous reproduction of the video data and the audio data are represented by the following expressions.YV÷VdV≧(Tf1+Tf2+Tf3+P×(Tfj+Tfi)+Ta+(P+2)×(a+b)×Ts)×Vt÷(Vt−VdV−VdA)YA÷VdA≧(Tf1+Tf2+Tf3+P×(Tfj+Tfi)+Ta+(P+2)×(a+b)×Ts)×Vt+(Vt−VdV−VdA)
Since the time for reproducing the data of YA is equal to the time for reproducing the data of YV,YA÷VdA=YV÷VdV. 
Since the time for reproducing the data of YcV is equal to the time for reproducing the data of YcA,YcV÷VdV=YcA÷YdA, YcV=TcV×Vt, andYcA=TcAa×Vt. 
In the above expressions, the letters represent the following.    P: Number of recorded areas which are completely continuously read in a cut-edited area (P≧0);    YV: Total size of the video data to be reproduced;    YA: Total size of the audio data to be reproduced;    VdV: Data rate of the video data;    VdA: Data rate of the audio data;    Tf1: Seek time from the recorded area G16 to the recorded area G17;    Tf2: Seek time from the recorded area G13 to the recorded area G18;    Tf3:.Seek time from the recorded area G18 to the recorded area G19;    Ta: Seek time from the recorded area G19 to the next recorded area;    a: Number of ECC blocks skipped in each of the recorded areas G16, G12 and G18 of the video data;    b: Number of ECC blocks skipped in each of the recorded areas G17, G13 and G19 of the audio data;    Ts: Time required for recording one ECC block;    Vt: Rate at which data is read from the information recording medium;    YcV: Size of the video data in the recorded area G12; and    YcA: Size of the audio data in the recorded area G13.
From the conditions for the simultaneous reproduction, the value of P is obtained. In consideration of the obtained value of P and the short-distance access time, the minimum size of the recorded area of each of the audio data and the video data is determined. Seamless reproduction is performed by recording the audio data and the video data in an interleaving manner such that the number of the recorded areas is smaller than the obtained value of P.
In the example of FIG. 17, the audio data and the video data are recorded discretely. In the case where the audio data and the video data are recorded in continuous areas, the seek operation between the audio data and the video data is not necessary. As a result, the conditions for seamless reproduction are alleviated (see, for example, Japanese Application No. 2002-252097 (FIGS. 17 and 20).
The above-described conventional art does not consider the delay time generated by the decoding operation of the compressed video data and audio data, or the variable bit rate. Therefore, there is a problem in that although the determination result that seamless reproduction of edited real time data is possible is obtained, actual reproduction does not result in seamless reproduction since the video data or audio data is interrupted.